Method and apparatus of accessing channel in wireless communication system

ABSTRACT

A method and apparatus of accessing a channel in a wireless communication system is provided. The method includes receiving a first frame including configuration information on a channel allocated from a bandwidth including a primary channel, a secondary channel and an extension channel from an access point (AP), and transmitting a second frame to the AP by using the allocated channel. The configuration information includes an extension channel offset element field that sets the extension channel as the offset of the primary channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/329,242, filed on Jul. 11, 2014, now U.S. Pat. No. 9,191,928, whichis a continuation of U.S. patent application No. 13/002,301, filed onDec. 30, 2010, now U.S. Pat. No. 8,811,312, which is the National Stagefiling under 35 U.S.C. 371 of International Application No.PCT/KR2009/003572, filed on Jul. 1, 2009, which claims the benefit ofearlier filing date and right of priority to Korean Application No.10-2008-0126486, filed on Dec. 12, 2008, and also claims the benefit ofU.S. Provisional Application Nos. 61/159,791, filed on Mar. 12, 2009,and 61/077,864, filed on Jul. 2, 2008, the contents of which are allhereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication, and moreparticularly, to a method and apparatus of accessing a channel in awireless communication system.

BACKGROUND ART

With the advancement of information communication technologies, variouswireless communication technologies have recently been developed. Awireless local access network (WLAN) is a technology whereby superhigh-speed internet access is possible in a region providing a specificservice by using a portable terminal such as a personal digitalassistant (PDA), a laptop computer, a portable multimedia player (PMP),etc.

Ever since the institute of electrical and electronics engineers (IEEE)802, i.e., a standardization organization for WLAN technologies, wasestablished in February 1980, many standardization works have beenconducted. Initially, WLAN used a frequency of 2.4 GHz to support a datarate of 1 to 2 Mbps by using frequency hopping, spread spectrum,infrared ray communication, etc. Recently, the WLAN can support a datarate of up to 54 Mbps by using orthogonal frequency divisionmultiplexing (OFDM). In addition, the IEEE 802.11 is developing orcommercializing standards of various technologies such as quality ofservice (QoS) improvement, access point (AP) protocol compatibility,security enhancement, radio resource measurement, wireless access invehicular environments, fast roaming, mesh networks, inter-working withexternal networks, wireless network management, etc.

The IEEE 802.11b standard supports a data rate of up to 11 Mbps (bitsper second) by using a frequency band of 2.4 GHz. The IEEE 802.11astandard uses a frequency band of 5 GHz instead of the frequency band of2.4 GHz and thus significantly reduces influence of interference. TheIEEE 802.11 a standard has improved the data rate to up to 54 Mbps byusing the OFDM technology. The IEEE 802.11n standard provides increasednetwork speed and reliability, extended coverage.

Basic access mechanism of an IEEE 802.11 is a carrier sense multipleaccess with collision avoidance (CSMA/CA) combined with binaryexponential backoff. The CSMA/CA mechanism is also referred to as adistributed coordinate function (DCF) and basically employs a “listenbefore talk” access mechanism. A station (STA) listens a wireless mediumbefore starting transmission. As a result of listening, if it is sensedthat the wireless medium is not in use, the listening STA starts itstransmission. Otherwise, if it is sensed that the wireless medium is inuse, the STA does not start its transmission but enters a delay durationdetermined by the binary exponential backoff algorithm. The CSMA/CAchannel access mechanism is not so efficient since throughput at the MAClayer provides only 50 to 60% of throughput at the physical layer.

IEEE 802.11 VHT (Very High Throughput) is one of WLAN systems which havebeen recently proposed to support throughput of higher than 1 Gbps. Twokinds of VHT system are independently progressed: one is IEEE 802.11 acbelow 6 GHz band and another is IEEE 802.11ac for 60 GHz band.

The VHT system is expected to use bandwidths broader than at least 60MHz. A AP simultaneously transmit data at different frequencies tomultiple STAs to increase the overall throughput.

A technique for efficiently operating a wideband VHT system is required.

DISCLOSURE OF INVENTION Technical Problem

The present invention provides a method and apparatus of accessing achannel to support wideband in a WLAN system.

Technical Solution

In an aspect, a method of accessing a channel in a wirelesscommunication system is provided. The method includes receiving a firstframe including configuration information on a channel allocated from abandwidth including a primary channel, a secondary channel and anextension channel from an access point (AP), and transmitting a secondframe to the AP by using the allocated channel, wherein the primarychannel and the secondary channel have bandwidths used by legacystations and the configuration information includes an extension channeloffset element field that sets the extension channel as the offset ofthe primary channel.

The configuration information may be an operation element and the firstframe may correspond to one of a beacon frame, a probe response frameand an association response frame. The first frame may be a channelswitch announcement frame.

In another aspect, a method of accessing a channel in a wirelesscommunication system is provided. The method includes selecting a firstchannel from a plurality of narrowband channels, starting a backofftimer if the selected first channel is idle, confirming whether anunselected second channel is idle if the backoff timer is expired, andtransmitting a frame through the first and second channels if the secondchannel is idle.

In still another aspect, a station for wireless communication includes aradio frequency (RF) unit to transmitting a radio signal, and aprocessor coupled with the RF unit and configured to select a firstchannel from a plurality of narrowband channels, start a backoff timerif the selected first channel is idle, confirm whether an unselectedsecond channel is idle if the backoff timer is expired, and transmit aframe through the first and second channels if the second channel isidle.

Advantageous Effects

A wideband channel is managed and used through a plurality of narrowbandchannels, and thus the efficiency of radio resources can be improved andthroughput can be increased.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing an exemplary structure of a wirelesslocal access network (WLAN) system to implement an embodiment of thepresent invention.

FIG. 2 illustrates exemplary channel management that combines threesubchannels to support a bandwidth of 60 MHz.

FIG. 3 illustrates exemplary channel management that combines foursubchannels to support a bandwidth of 80 MHz.

FIG. 4 illustrates an exemplary format of an operation element forsetting up multiple channels.

FIG. 5 illustrates an exemplary channel switch announcement frameaccording to an embodiment of the present invention;

FIG. 6 illustrates an exemplary extended channel switch announcementframe according to an embodiment of the present invention;

FIG. 7 illustrates exemplary channel allocation for hierarchical channelaccess;

FIG. 8 illustrates an exemplary operation element;

FIG. 9 is a flowchart showing a hierarchical channel access mechanismaccording to an embodiment of the present invention;

FIG. 10 illustrates an example of channel allocation for hierarchicalchannel access;

FIG. 11 illustrates another example of channel allocation forhierarchical channel access; and

FIG. 12 is a block diagram of a wireless communication system toimplement an embodiment of the present invention.

MODE FOR THE INVENTION

FIG. 1 is a schematic view showing an exemplary structure of a wirelesslocal access network (WLAN) system to implement an embodiment of thepresent invention. The WLAN system includes one or more basis servicesets (BSSs). The BSS is a set of stations (STAs) which are successfullysynchronized to communicate with one another. The BSS can be classifiedinto an infrastructure BSS and an independent BSS (IBSS). Theinfrastructure BSSs (BSS1 and BSS2) shown in FIG. 1 include STAs 10, 30and 40, access points (APs) 20 and 50. The AP is a STA providing adistribution service. The APs 20 and 50 are connected by means of adistribution system (DS). The IBSS operates as Ad-hoc mode and does notinclude any AP. The IBSS constitutes a self-contained network sinceconnection to the DS is not allowed. A plurality of infrastructure BSSscan be interconnected by the use of the DS. An extended service set(ESS) is a plurality of BSSs connected by the use of the DS. In the sameESS, a non-AP STA can move from on BSS to another BSS while performingseamless communication.

The STA is an arbitrary functional medium including a medium accesscontrol (MAC) and wireless-medium physical layer (PHY) interfaceconforming to the institute of electrical and electronics engineers(IEEE) 802. 11 standard. The STA may be an AP or a non-AP STA. A non-APSTA may be a portable terminal operated by a user. The non-AP STA may besimply referred to as an STA. The non-AP STA may be referred to as awireless transmit/receive unit (WTRU), a user equipment (UE), a mobilestation (MS), a mobile terminal, a mobile subscriber unit, etc. The APis a functional entity for providing connection to the DS through awireless medium for an associated STA. Although communication betweennon-AP STAs in an infrastructure BSS including the AP is performed viathe AP in principle, the non-AP STAs can perform direct communicationwhen a direct link is set up. The AP may be referred to as a centralizedcontroller, a base station (BS), a node-B, a base transceiver system(BTS), a site controller, etc.

A VHT (Very High Throughput) WLAN system aims to be reflected on one ofIMT (International Mobile Telecommunication)-Advanced technologiescorresponding to fourth-generation telecommunication standard.Accordingly, the VHT WLAN system is required to operate in IMT-Advancedcandidate bands and the existing 2.4 GHz and 5 GHz bands.

The VHT WLAN system is required to use a bandwidth wider than at least60 MHz in order to secure throughput higher than 1 Gbps. To segment awideband into a plurality of narrowbands and use the narrowbands isefficient more than to use the wideband as a single channel in terms ofbackward compatibility and resource efficiency.

Hereinafter, a narrowband channel having a bandwidth of 20 MHz isreferred to as a subchannel. A technique of binding three or foursubchannels to support a bandwidth of 60 MHz or 80 MHz will now bedescribed. The number of subchannels, the bandwidth of the subchanneland the overall bandwidth are exemplary purpose only.

FIG. 2 illustrates exemplary channel management that combines threesubchannels to support a bandwidth of 60 MHz. The three subchannelsinclude a primary channel and two extension channels. The primarychannel is set in order to secure backward compatibility with STAs(hereinafter referred to as legacy STAs) supporting standards of lowerthan IEEE 802.11n using a bandwidth of 20 MHz. Legacy STAs supporting 20MHz use the primary channel preferentially. STAs supporting 40 MHz or 60MHz can use the primary channel, two extension channels and/or acombination thereof.

Subfigure (a) of FIG. 2 shows that the extension channels using 20 MHzare located in a frequency band lower than the primary channel. Here,the two 20 MHz extension channels can be set as a single 40 MHzextension channel. Subfigure (b) of FIG. 2 shows that the two extensionchannels are located in a frequency band higher than the primarychannel. The two 20 MHz extension channels can be set as a single 40 MHzextension channel. Subfigure (c) of FIG. 2 shows that the primarychannel is located between the two extension channels.

In (a) and (b) of FIG. 2, the multiple channels can be administrated byusing the primary channel and the single 40 MHz extension channelcontiguous to the primary channel. In (c) of FIG. 2, the multiplechannels can be administrated by the primary channel and two 20 MHzextension channels contiguous to the primary channel.

An AP can set a subchannel among overall available channels as a primarychannel and use the primary channel as a common channel for controlsignal. The AP can set a bandwidth of an extension channel to one of 20MHz, 40 MHz and 60 MHz according to channel availability if a STAsupports the extension channel.

FIG. 3 illustrates exemplary channel management that combines foursubchannels to support a bandwidth of 80 MHz. The four subchannelsinclude a primary channel, a secondary channel and two extensionchannels. The primary channel and the secondary channel are set in orderto secure backward compatibility with legacy STAs supporting standardsof lower than IEEE 802.11 n using 40 MHz. Legacy STAs supporting 20 MHzpreferentially use the primary channel and use the secondary channelwhen the primary channel is being used. Legacy STAs supporting 40 MHzpreferentially use the primary channel and the secondary channel. STAssupporting bandwidths higher than 60 MHz can use the primary channel,the secondary channel, the extension channels and/or a combinationthereof.

Subfigure (a) of FIG. 3 shows that the extension channels having 20 MHzare located in a frequency band lower than the primary channel and thesecondary channel. The primary channel is located in the highest bandand the secondary channel is located below the primary channel. Here,the two 20 MHz extension channels can be set as a single 40 MHzextension channel. Subfigure (b) of FIG. 3 shows that the 20 MHzextension channels are located in a frequency band higher than theprimary channel and the secondary channel. The primary channel islocated in the lowest band and the secondary channel is located abovethe primary channel. Here, the two 20 MHz extension channels can be setas a single 40 MHz extension channel. Subfigure (c) of FIG. 3 shows thatthe primary channel and the secondary channel are located between thetwo extension channels. The primary channel is located in a band higherthan the secondary channel. Subfigure (d) of FIG. 3 shows that theprimary channel and the secondary channel are located between the twoextension channels. The primary channel is located in a band lower thanthe secondary channel.

In (a) and (b) of FIG. 3, the multiple channels can be administrated byusing the primary channel, the secondary channel and a extension channelhaving 40 MHz. In (c) and (d) of FIG. 3, the multiple channels can beadministrated by using the primary channel, the secondary channel andtwo extension channels each having 20 MHz.

A method of setting and changing multiple channels will now bedescribed.

FIG. 4 illustrates an exemplary format of an operation element forsetting up multiple channels. An operation element 400 for settingmultiple channels includes an element ID 410, a primary channel field420, a secondary channel offset field 430, an extension channel offsetfield 440 and a channel width field 450. The element ID 410 is anidentifier for identifying the operation element 400. The primarychannel field 420 indicates the position of a primary channel in theavailable bandwidth of a system and can be represented as a channelnumber. The channel width field 450 represents a channel bandwidthsupported by a STA or a channel bandwidth used for transmission. The STAcan support at least one of bandwidths 20 MHz, 40 MHz, 60 MHz and 80MHz.

The secondary channel offset field 430 indicates the offset of thesecondary channel relative to the primary channel. The secondary channeloffset field 430 can be configured as represented by Table 1.

TABLE 1 Value Name Description 0 SCN (No Secondary No secondary channelis present. Channel) 1 SCA (Secondary Channel The secondary channel isabove the Above) primary channel. 2 SCB (Secondary Channel The secondarychannel is below the Below) primary channel.

The extension field offset field 440 indicates the position of anextension channel relative to the primary channel and/or the secondarychannel. The value of the extension channel offset field 440 can be setbased on the primary channel, as represented by Table 2.

TABLE 2 Value Name Description 0 ECN (No Extension No extension channelis present. Channel) 1 ECA (Extension Channel The extension channel isabove the Above) primary channel. 2 ECB (Extension Channel The extensionchannel is below the Below) primary channel. 3 ECC (Extension ChannelThe primary channel is in between the Cross) extension channels.

Though Table 2 shows that the extension channel offset field 440indicates the position of the extension channel based on the primarychannel, the extension channel offset field 440 may indicate theposition of the extension channel based on the secondary channel orbased on a combination of the primary channel and the secondary channel.

The terms and values represented in Tables 1 and 2 are exemplary andthose who skilled in the art can easily change the terms and values.

All the aforementioned fields are not included in the operation element400. Some of the fields may be omitted or other fields may be added. Forexample, the operation element 400 may not include the secondary channeloffset field 430 if the secondary channel is not used.

The operation element 400 may be included in at least one of a beaconframe, a probe response frame and an association response frame andtransmitted from an AP to a STA. Above frames may be referred to section7.2.3 of IEEE standard P802. 11-REVma/D9.0 “Wireless LAN Medium AccessControl (MAC) and physical layer (PHY) specifications” which is herebyincorporated by reference.

An AP that classifies 60 MHz, 80 MHz or wider bandwidth as a primarychannel, a secondary channel and an extension channel and manages thechannels is required to change a channel previously allocated thereto inconsideration of channel status. For example, if considerable noise isgenerated or/and interference with other signals occurs in a subchannelused as a primary channel in the overall channel bandwidth, anothersubchannel is updated to the primary channel to efficiently manage aWLAN system.

FIG. 5 illustrates an exemplary channel switch announcement frameaccording to an embodiment of the present invention. A channel switchannouncement frame 500 is used by an AP in a BSS or a STA in an IBSS toadvertise when it is changing to a new channel. The channel switchannouncement frame 500 includes a category field 510, an action valuefield 520, a channel switch announcement element field 530, a secondarychannel offset element field 540, and an extension channel offsetelement field 550. The category field 510 may represent spectrummanagement. The action value field 520 may represent a channel switchannouncement frame.

The channel switch announcement element field 530 includes an element ID531, a length field 532, a channel switch mode field 533, a new channelnumber field 535 and a channel switch count field 536. The channelswitch mode field 533 indicates any restrictions on transmission until achannel switch. An AP in a BSS or a STA in an IBSS may set the channelswitch mode field 533 to either 0 or 1 on transmission. The channelswitch mode field 533 set to 1 means that the STA in a BSS to which theframe containing the element is addressed transmits to further frameswithin the BSS until the scheduled channel switch. The channel switchmode field 533 set to 0 does not impose any requirement on the receivingSTA. The new channel number field 535 is set to the number of thechannel to which the STA is moving. The channel switch count field 536either is set to the number of target beacon transmission times (TBTTs)until the STA sending the channel switch announcement element switchesto the new channel or it set to 0. A value of 1 indicates that theswitch shall occur immediately before the next TBTT. A value of 0indicates that the switch occurs at any time after the frame containingthe element is transmitted.

The secondary channel offset element field 540 includes an element ID541, a length field 542 and a secondary channel offset field 543. Thesecondary channel offset element field 540 represents information on anew secondary channel when the secondary channel is changed to the newsecondary channel. The secondary channel offset field 543 may be set asrepresented by Table 1.

The extension channel offset element field 550 includes an element ID551, a length field 552 and an extension channel offset field 553 andrepresents information on a new extension channel when the extensionchannel is changed to the new extension channel. The extension channeloffset field 553 may be set as represented by Table 2.

FIG. 6 illustrates an exemplary extended channel switch announcementframe according to an embodiment of the present invention. An extendedchannel switch announcement frame 600 is used by an AP in a BSS or a STAin an IBSS to advertise when it is changing to a new channel or a newchannel in a new regulatory class. The extended channel switchannouncement frame 600 includes a category field 610, an action valuefield 620, an extended channel switch announcement element field 630, asecondary channel offset element field 640 and an extension channeloffset element field 650.

Compared with the channel switch announcement frame 500 in FIG. 5, theextended channel switch announcement frame 600 includes the extendedchannel switch announcement element field 630 which further includes anew regulatory class field 634. The new regulatory class field 634 isset to the number of the regulatory class after the channel switch. Anew channel number field 635 is set to the number of the channel afterthe channel switch. The channel number is a channel from the STA's newregulatory class.

The secondary channel offset element field 640 and the extension channeloffset element field 650 can be set in the same manner in which thesecondary channel offset element field 540 and the extension channeloffset element field 550 of the channel switch announcement frame 500shown in FIG. 5 are set.

A hierarchical channel access mechanism in a system including multiplesubchannels will now be described. Hierarchical channel accessrepresents an attempt to perform channel access according to multipleclasses.

FIG. 7 illustrates exemplary channel allocation for hierarchical channelaccess. The overall bandwidth of 80 MHz is divided into two bondingchannels, that is, a primary bonding channel 710 and a secondary bondingchannel 720. The primary bonding channel 710 and the secondary bondingchannel 720 respectively have a bandwidth of 40 MHz and include two 20MHz subchannels. The primary bonding channel 710 includes a primarychannel 711 and a secondary channel 712 and the secondary bondingchannel 720 includes a primary channel 721 and a secondary channel 722.The primary channels 711 and 721 and the secondary channels 712 and 722are exemplary and their positions may be changed.

If a STA connected to a VHT system supports only a channel bandwidth of20 MHz, channels are allocated such that the STA operates in a primarychannel. The primary channel 711 of the primary bonding channel 710 orthe primary channel 712 of the secondary bonding channel 720 may beallocated. Otherwise, the primary channel 711 of the primary bondingchannel 710 may be given priority.

If the STA connected to the VHT system supports a channel bandwidth of40 MHz, the channels are allocated such that STA operates in the primarybonding channel 710 or the secondary bonding channel 720. Otherwise, theprimary bonding channel 710 may be given priority.

An AP sets channels that will be used by STAs based on channelbandwidths supported by the STAs. Channel set-up may be processedthrough an association response frame and channel switch may beprocessed through a channel switch announcement frame. For example, whena STA supporting a channel bandwidth of 80 MHz is connected to the AP,the AP may use the primary channel field 420 of the operation element400 included in the association response frame for allocation of theprimary bonding channel 710 and use the secondary channel offset field430 for allocation of the secondary bonding channel 720. It is possibleto add a new field to the operation element or change the existingfields in order to allocate the primary bonding channel 710 and thesecondary bonding channel 720. Furthermore, the AP may send the channelswitch announcement frame 500 or the extended channel switchannouncement frame 600 to switch the primary bonding channel 710 and thesecondary bonding channel 720 to each other. Accordingly, the AP canachieve load balancing for STAs on the channel bandwidth of 80 MHz.

FIG. 8 illustrates an exemplary operation element. An operation element800 includes a primary channel field 810 of a primary bonding channel, asecondary channel field 830 of the primary bonding channel, a primarychannel field 840 of a secondary bonding channel and a secondary channelfield 850 of the secondary bonding channel. An AP may inform STAs whichsubchannel of which bonding channel is allocated through the operationelement 800.

A STA supporting a channel bandwidth of 80 MHz (more specifically, anon-AP STA supporting VHT) may use four 20 MHz channels, two 40 MHzchannels or a single 80 MHz channel. That is, both the primary bondingchannel 710 and the secondary bonding channel 720 are allocated to theSTA, and the STA may use the primary bonding channel 710 and thesecondary bonding channel 720 as a 80 MHz channel or use one of theprimary bonding channel 710 and the secondary bonding channel 702 as a40 MHz channel. The STA may use channels based on CCA (Clear ChannelAssessment) information.

FIG. 9 is a flowchart showing a hierarchical channel access mechanismaccording to an embodiment of the present invention. The hierarchicalchannel access mechanism may be performed by a STA. A STA supporting achannel bandwidth of 80 MHz selects a primary bonding channel or asecondary bonding channel (S910). The STA confirms whether the selectedbonding channel is idle (S920). When the selected bonding channel isidle, the STA performs backoff (S930). After a backoff timer is started,the STA confirms whether the unselected bonding channel is idle when thebackoff timer is expired (S940). When the unselected bonding channel isidle, the STA transmits frames by using the two bonding channels, thatis, a channel having 80 MHz (S940). When the unselected bonding channelis not idle, the STA transmits frame by using the selected bondingchannel (S950).

If the STA supporting the channel bandwidth of 80 MHz wants to use a 40MHz channel, the STA may confirm whether the channel is used as follows.The STA randomly selects one of the primary bonding channel and thesecondary bonding channel. When the selected bonding channel is idle,the STA performs backoff. After the backoff timer is started, the STAconfirms whether the secondary channel is idle when the backoff timer isexpired. When the secondary channel is idle, the STA transmits frames byusing the selected bonding channel. When the secondary channel is notidle, the STA transmits frames by using the primary channel.

FIG. 10 illustrates an example of channel allocation for hierarchicalchannel access. A bandwidth of 60 MHz is segmented into two bondingchannels, that is, a primary bonding channel 1010 and a secondarybonding channel 1020. The primary bonding channel 1010 and the secondarybonding channel 1020 respectively have a bandwidth of 40 MHz and includetwo 20 MHz subchannels. The primary bonding channel 1010 includes aprimary channel 1011 and a secondary channel 1012 and the secondarybonding channel 1020 includes a primary channel 1021 and a secondarychannel 1022. The secondary channel 1012 of the primary bonding channel1010 and the secondary channel 1022 of the secondary bonding channel1020 overlap each other.

If a STA connected to a VHT system supports only a channel bandwidth of20 MHz, a channel is allocated to the STA such that the STA operates ina primary channel. The primary channel 1011 of the primary bondingchannel 1010 or the primary channel 1012 of the secondary bondingchannel 1020 may be allocated to the STA. Otherwise, the primary channel1011 of the primary bonding channel 1010 may be given priority.

If the STA connected to the VHT system supports a channel bandwidth of40 MHz, a channel is allocated to the STA such that the STA operates inthe primary bonding channel 1010 or the secondary bonding channel 1020.Otherwise, the primary bonding channel may be given priority. Theprimary bonding channel 1010 and the secondary bonding channel 1020cannot be simultaneously used because the primary bonding channel 1010and the secondary bonding channel 1020 overlap each other.

An AP sets channels that will be used by STAs based on channelbandwidths supported by the STAs. Channel set-up may be processedthrough an association response frame and channel switch may beprocessed through a channel switch announcement frame.

A STA supporting a channel bandwidth of 60 MHz may select and use one ofa 20 MHz subchannel, a 40 MHz channel and a 60 MHz channel based on CCAinformation. The STA supporting the channel bandwidth of 60 MHz selectsa primary bonding channel or a secondary bonding channel. The STAconfirms whether the selected bonding channel is idle. When the selectedbonding channel is idle, the STA performs backoff. After a backoff timeris started, the STA confirms whether the unselected bonding channel isidle when the backoff timer is ended. When the unselected bondingchannel is also idle, the STA transmits frames by using the two bondingchannels, that is, a channel having a bandwidth of 60 MHz. When theunselected bonding channel is not idle, the STA transmits frames byusing the selected 40 MHz bonding channel.

If the STA supporting the channel bandwidth of 60 MHz wants to use a 40MHz channel, the STA confirms whether the channel is used as follows.The STA selects one of the primary bonding channel and the secondarybonding channel. When the primary channel of the selected bondingchannel is idle, the STA executes backoff. After the backoff timer isstarted, the STA confirms the secondary channel of the selected bondingchannel is idle when the backoff timer is ended. If the secondarychannel is idle, the STA transmits frames by using the selected bondingchannel. If the secondary channel is not idle, the STA transmits frameby using the primary channel.

A first channel is randomly selected from a plurality of narrowbandchannels. Alternatively, the first channel may be selected based onconfiguration information from an AP. When the first channel is idle, itis confirmed whether a second channel is idle after the lapse of backofftime. When the second channel is idle, frames are transmitted using thefirst and second channels. The second channel may be contiguous to thefirst channel, and thus a wideband channel can be supported bynarrowband channels.

FIG. 11 illustrates another example of channel allocation forhierarchical channel access. A bandwidth of 60 MHz is segmented into twobonding channels, that is, a primary bonding channel 1110 and asecondary bonding channel 1120. The primary bonding channel 1110 and thesecondary bonding channel 1120 respectively have a bandwidth of 40 MHzand include two 20 MHz subchannels. The primary bonding channel 1110includes a primary channel 1111 and a secondary channel 1112 and thesecondary bonding channel 1120 includes a primary channel 1121 and asecondary channel 1122. Compared with the embodiment shown in FIG. 10,the primary channel 1111 of the primary bonding channel 1110 and thesecondary channel 1122 of the secondary bonding channel 1120 overlapeach other. The aforementioned channel access mechanism may be usedwithout being changed.

FIG. 12 is a block diagram of a wireless communication system toimplement an embodiment of the present invention is implemented. An AP150 includes a processor 151, a memory 152 and an RF (Radio Frequency)unit 153. The processor 151 implements a proposed function, processand/or method. Channel allocation and channel switch can be performed bythe processor 151. The memory 152 is operatively connected to theprocessor 151 and stores information for operating the processor 151.The RF unit 153 is operatively connected to the processor 151 andtransmits and/or receives RF signals. A STA 160 includes a processor161, a memory 162 and an RF unit 163. The processor 161 implements aproposed function, process and/or method. The aforementioned channelaccess method can be implemented by the processor 161. The memory 162 isoperatively connected to the processor 161 and stores information foroperating the processor 161. The RF unit 163 is operatively connected tothe processor 161 and transmits and/or receives RF signals.

The processors 151, 161 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 152, 162 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The RF units 153, 163 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 152, 162 and executed by processors 151, 161. The memories 152,162 can be implemented within the processors 151, 161 or external to theprocessors 151, 161 in which case those can be communicatively coupledto the processors 151, 161 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the spirit and scope ofthe appended claims.

What is claimed is:
 1. A method of accessing a channel in a wirelesscommunication system, the method comprising: receiving channelinformation from an access point (AP), the channel information includinga secondary channel offset element and an extension channel offsetelement, the secondary channel offset element indicating a position of asecondary channel relative to a primary channel, the extension channeloffset element indicating a position of at least one extension channel;and performing a communication with the AP by using the primary channel,the secondary channel and the extension channel, wherein the secondarychannel offset element is set to a value indicating one of first, secondand third values, the first value indicating that no secondary channelis present, the second value indicating that the secondary channel isabove the primary channel, the third value indicating that the secondarychannel is below the primary channel, wherein the extension channeloffset element is set to a value indicating one of first and secondvalue, the first value indicating that the secondary channel and theprimary channel are located below or above two extension channels, thesecond value indicating that the secondary channel and the primarychannel are located between two extension channels.
 2. The method ofclaim 1, wherein the channel information is received in a channel switchannouncement frame to advertise a channel switch.
 3. The method of claim2, wherein the channel switch announcement frame further includes achannel switch announcement element indicating when the channel switchoccurs.
 4. The method of claim 1, wherein a bandwidth of the primarychannel is same as a bandwidth of the secondary channel.
 5. A device foraccessing a channel in a wireless local area network, the devicecomprising: a radio frequency unit configured to transmitting a radiosignal; and a processor coupled with the radio frequency unit andconfigured to: instruct the radio frequency unit to receive channelinformation from an access point (AP), the channel information includinga secondary channel offset element and an extension channel offsetelement, the secondary channel offset element indicating a position of asecondary channel relative to a primary channel, the extension channeloffset element indicating a position of at least one extension channel;and instruct the radio frequency unit to perform a communication withthe AP by using the primary channel, the secondary channel and theextension channel, wherein the secondary channel offset element is setto a value indicating one of first, second and third values, the firstvalue indicating that no secondary channel is present, the second valueindicating that the secondary channel is above the primary channel, thethird value indicating that the secondary channel is below the primarychannel. wherein the extension channel offset element is set to a valueindicating one of first and second value, the first value indicatingthat the secondary channel and the primary channel are located below orabove two extension channels, the second value indicating that thesecondary channel and the primary channel are located between twoextension channels.
 6. The device of claim 5, wherein the channelinformation is received in a channel switch announcement frame toadvertise a channel switch.
 7. The device of claim 6, wherein thechannel switch announcement frame further includes a channel switchannouncement element indicating when the channel switch occurs.
 8. Thedevice of claim 5, wherein a bandwidth of the primary channel is same asa bandwidth of the secondary channel.